1. Field of the Invention
The invention relates to a bearing apparatus in which a bearing part is formed by a mutually opposed rotating member and a fixed member, and to a method for manufacturing such a bearing apparatus.
2. Related Background Art
Bearings are widely used in various rotational drive apparatuses and the like. An example of such a bearing is a fluid dynamic bearing, in which a rotating member is supported by developing a dynamic pressure in a lubricating fluid. This bearing apparatus is provided with a thrust bearing part SB and a radial bearing part RB, as shown in FIG. 16 of the accompanying drawings.
Referring to FIG. 16, a rotating member (rotating hub) 3 is joined to a rotating shaft 2, which is supported by a fluid dynamic bearing member (bearing sleeve) 1. The bearing sleeve 1 serves as a fixed member. The end face of the rotating member 3 in the axial direction near the central region thereof (lower side as shown in FIG. 16) and the axial-direction outer end face of the fluid dynamic bearing member 1 (upper side in FIG. 16) are mutually opposed, so as to form an opposing thrust bearing interface. This thrust bearing forms a fluid dynamic thrust bearing part SB.
An appropriate lubrication fluid (not shown in the drawing) is injected inside the bearing space in the fluid dynamic thrust bearing part SB, and a spiral dynamic pressure generating groove is formed in the circumferential direction as a means for generating dynamic pressure in the lubricating fluid. The dynamic pressure-generating groove generates a dynamic pressure relative to the above-noted lubrication fluid by pressurizing action acting in the direction of the arrow, thereby achieving the desired thrust floating force.
In the radial bearing interface at which the inner peripheral wall surface of the fluid dynamic bearing member 1 and the outer peripheral wall surface of the rotating member 2 are in mutual opposition, radial bearing parts RB are formed at two locations along the axial direction. On the inside of each of the fluid dynamic radial bearing parts SB is injected a lubrication fluid (not shown in the drawing), which is continuous with the lubrication fluid of the fluid dynamic thrust bearing part SB. Herringbone shaped dynamic pressure-generating grooves, for example, are formed in a row in the circumferential direction as a means of generating dynamic pressure in the lubrication fluid. The dynamic pressure-generating grooves generate a dynamic pressure in the lubrication fluid by a pressurizing action in the direction of the arrow, thereby achieving the desired radial floating force.
In order to reduce the coefficient of friction between the opposing surfaces in the of bearing interface formed by the rotating member 2 and the fixed member 1 of the bearing apparatus described above, a coating or the like of a resin sliding film is applied thereto. The resin material forming the resin sliding film is, for example, a polyamide-based or epoxy-based material, and particles of a solid lubricant such as PTFE, molybdenum disulfide, or graphite or the like are often further disbursed in the resin material. Methods of forming the resin slide material generally include electrodeposition, immersion, the pulling method, painting, spraying, and printing.
None of these methods forming the resin sliding film in the past were capable of forming the resin sliding film with a high degree of accuracy and low cost.
In the case of immersion, for example, there is a large variation in the thickness of the film that is formed, thereby requiring subsequent processing to achieve film thickness accuracy. In addition, it is necessary to use a process step of forming a mask at locations not requiring the film, as well as a process step of removing this mask, thereby inevitably resulting in an expensive manufacturing process.
In the case of using electrodeposition, although it is relatively easy to control the film thickness, the limit to the variation in film thickness is ±5 μm to ±10 μm, thereby limiting the accuracy that can be achieved. Additionally, as in the case of the immersion method, it is necessary to use a process step of forming a mask at locations not requiring the film, and a process step of removing the mask, thereby resulting in an expensive manufacturing process.
With the spray method as well, there is a large variation in the thickness of the film that is formed, thereby requiring subsequent processing to achieve film thickness accuracy, as well as the need to use a process step of forming a mask at locations not requiring the film, and a process step of removing the mask, thereby inevitably resulting in an expensive manufacturing process.
Using the painting method, because a dispenser or the like is used to paint onto prescribed locations, there is no need to form a mask or the like. However, there is a large variation in the thickness of the film that is formed. Additionally, a spinner capable of improving the film thickness accuracy is not usable with a large, complex surface area that is not flat, such as in a bearing apparatus. Even if such a spinner were to be used, an additional step is required to remove resin that is splattered by a centrifugal force, thereby making the manufacturing process expensive.
In all of the above-noted methods, because there is a large amount of material wasted, there is a limitation imposed on the improvement of productivity. In the down-stream processing made necessary by an increase in the variation in the thickness of the resin sliding film that is formed, a cutting burr can remain at locations from which excess resin has been removed, and the peeling away of this burr, which can then float, can cause problems with rotation.
In the case of using the method of printing, screen printing is usually employed. With screen printing, however, it is only possible to print on a flat or cylindrical surface that can be brought into intimate contact with the screen. There is thus the problem of not being able to apply screen printing to surfaces having complex shapes, as in bearing apparatuses. For example, in a conventional fluid dynamic bearing under the premise that it is difficult to directly coat a resin slide film onto a surface of a thrust bearing part, a thin metal sheet is pre-coated with resin and then adhered to the main unit. In this case, however, it is clear that the cost of both parts and labor is high.
Given the above situation, the present invention provides a bearing apparatus in which it is possible to simply and efficiently form a resin sliding film on the opposing surfaces forming a bearing part.